Foaming and bulking are widespread problems that negatively impact the activity of wastewater treatment facilities worldwide. Wastewater treatment plants are utilized by municipalities, in industry, and by agricultural operations for the treatment and disposal of liquid and wet wastes. Commonly treated wet and liquid wastes include human wastes, wet wastes from industry including food, manufacturing, energy, chemical, mining and heavy industries, as well as the liquid animal and chemical wastes generated by agricultural and defense-related activities. An activated sludge process, nominally consisting of aeration tank(s) or basin(s) and settling tanks, is frequently used in wastewater treatment regimes. The activated sludge process is microbiological, relying on complex consortia of micro- and macro-organisms to convert the undesirable waste components into forms acceptable for disposal.
Ubiquitous challenges that negatively impact the activated sludge process are the related phenomena of bulking and foaming. Bulking is characterized by the poor settleability of activated sludge. Foaming is characterized by large volumes of foams and solids that accumulate on the surface of aeration basins and settling tanks. Foaming not only forms a physical nuisance by interfering with normal mechanical systems but also hinder biological activities through decreasing oxygen transfer efficiencies and by trapping waste gasses. Foaming and bulking may be chronic or periodic problems for wastewater plant systems. In some instances, large volumes of foam may be dispersed throughout the plant: in aerators, sedimentation basins and, in extreme cases, outside the premises all the way into the car park or surrounding areas Apart from the nuisance, bulking sludge and foam decrease the efficiency of the plant and may also make it difficult to achieve the required performance criteria, which is costly to the plant.
Bulking and foaming at wastewater treatment facilities is frequently associated with the presence of filamentous bacteria. Filamentous bacteria, as the term implies, are bacteria that grow in branched or unbranched filaments that range from several to hundreds of microns in length. Filamentous bacteria are an important component of healthy activated sludge as low levels of filaments are required for proper floc formation and settling of solids. Flocs contain both filamentous and non-filamentous bacteria. Problems can arise in the system when there is an over abundance of filamentous organisms. Filamentous bacteria promote bulking when filaments extend from one floc particle to another and form interfloc bridging or when there are filament-associated voids in the floc that increase buoyancy. Very large floc mats may also form into a floating scum that interferes with settling of sludge solids. Filamentous bacteria promote foaming due in part to the stabilizing effect of hydrophobic cells and surfactants have on the partitioning and stabilizing of gas bubbles.
A variety of methods are used to counter foaming and bulking within wastewater treatment facilities. However, none of the currently available methods are completely effective and the down time and loss of plant efficiency while dealing with foaming problems results in environmental risks and increased costs. These control methods including chemical antifoaming agents, physical control of foams, forceful chlorinated water sprays, and return sludge chlorination. Additionally, biological control treatments are commercially available. These are typically based on application of bacteria capable of suppressing filamentous bacteria. One of the confounding issues in developing anti-foaming and bulking treatments is the concern about specific control of the filamentous bacteria without disrupting the general microbial population involved in water remediation. Therefore, strong, non-discriminate biocides are not an appropriate option. Plant design, including aeration basin flow and aeration characteristics, is well known to affect the degree to which foaming and bulking occur. Ideally, all plants should be constructed in such a way as to limit foaming and bulking. However, replacing existing facilities is not always feasible and there will be a need to control foaming and bulking as long as plants that experience periodic foaming and bulking issues remain in operation. There is an ongoing need to develop new methods to control filamentous bacteria associated foaming within the wastewater treatment industry.
A treatment designed to reduce filamentous bacterial levels to non-problem levels without disrupting other microbiological events in the treatment plant constitutes the ideal control method. Bacteriophages, or phages, have the potential to be this ideal control agent. Phages are the ubiquitous and natural viral predators of bacteria. During the lytic infection process, a phage recognizes its specific host bacteria and injects the genomic DNA into the host cell. New phage particles are assembled, ˜100 per host cell, over the course of minutes to several hours. Phage encoded proteins produce catastrophic disintegration of the bacterial cell in a process termed lysis. Lysis kills the host cell and disperses progeny phage into the environment where they can adsorb to new bacterial hosts and begin the process again. The phage/host relationship is very specific: only certain species or strains of bacteria are targeted by any one phage. Phages are remarkably abundant in the environment, more so than bacteria. This abundance is mirrored by extremely high diversity. Because of their ubiquity, their specificity for bacterial cells, and their lack of interaction with human, animal, or plant cells, phages have been assigned the status of generally regarded as safe (GRAS). The bacteriolytic, yet extremely specific, nature of phages can be utilized to control the population of foaming and bulking associated filamentous bacteria without disrupting the overall microbial population.